1. Field of the Invention
The present invention relates to a traffic information display system mounted on a vehicle such as an automobile to present map information, etc. to the user, e.g. a driver.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional traffic information display system mounted on an automobile, disclosed in Japanese Patent Laid Open No. 11985/88 for example. In the same figure, the reference numeral 11 denotes an earth magnetism sensor for detecting an earth magnetism and thereby detecting an advancing direction of the vehicle; numeral 12 denotes an angular velocity sensor for detecting an angular velocity of the vehicle; numeral 13 denotes a running distance sensor for detecting a running distance of the vehicle; and numeral 14 denotes a global positioning system (GPS) which receives radio waves from plural artificial satellites and checks the present position, etc.
Numeral 20 denotes a system controller. The system controller 20 includes an interface 21 which receives outputs of the earth magnetism sensor 11, etc.; a CPU 22 which performs, for example, the calculation of a moving distance of the vehicle; a ROM 23 in which is stored a program to be executed by the CPU 22; a RAM 24 for temporarily storing data necessary for the execution of the program; a recording medium 25 constituted by, for example, CD-ROM or IC card, with digitized map information (map data) stored therein; a graphic memory 26 constituted by a video RAM for example; and a graphic controller 27 which prepares a map in the graphic memory 26 on the basis of graphic data fed from the CPU 22 and displays the map on a display unit 5. Numeral 28 denotes an input device, e.g. keyboard.
FIG. 2(A) shows an example of map data stored in the recording medium 25. This data is concerned with one area (called "unit") after the division of a predetermined area into a predetermined number of small areas (e.g. 256 areas). A navigation ID is an ID of this unit. The map data has such a hierarchical structure as shown in FIG. 2(B).
A road section table, an intersection table and three picture ID areas, which are shown in FIG. 2(A), are tables for control, and other road section data, etc. are effective map data.
A polygon data shown in the same figure is prepared in such a manner as illustrated in FIG. 3. A sea-land boundary in the unit, the contour of a park, etc. are approximated polygonally, and coordinates of the vertex of the polygon are determined as polygon data. A line data shown in FIG. 2(A) is prepared in such a manner as illustrated in FIG. 4. Roads, railway, etc. in the unit are approximated as a polygonal line and coordinates of the vertex of the polygonal line are determined as line data. Coordinates of intersections in the unit are used as intersection data. Further, coordinates and the kind of characters and letters required in the unit serve as character data and letter data.
The unit is divided into a large number of sections (e.g. 16). A set of start point coordinates and end point coordinates of straight lines representing roads, etc. in each section serves as road section data, and a set of coordinates of intersections in each section serves as intersection section data. In the road section table a leading address is set in the recording medium 25 of the road section data corresponding to each section. In the intersection section table a leading address is set in the recording medium 25 of the intersection section data corresponding to each section. In the three picture ID areas address data showing the polygon data portion, line data portion, character data portion and letter data portion are set which are required in the case of displaying the unit on respective scales.
The operation of this conventional system will now be described. The CPU 22 receives outputs of the earth magnetism sensor 11, angular velocity sensor 12, running distance sensor 13 and GPS 14 through the interface 21, then calculates the present position and a running direction of the vehicle on the basis of those outputs and the intersection data stored in the recording medium 25.
Next, the CPU 22 determines the unit in which the present position of the vehicle is present, and prepares a map according to the scale which has been input from the input device 28. In other words, the CPU inputs polygon data, etc. of that unit and prepares a map on the basis of those data. Further, a symbol representing the present position of the vehicle is added onto the map. Then, graphic data which constitute the map thus prepared are output to the graphic controller 27, which in turn plots images onto the information graphic memory 26 on the basis of the graphic data thus provided. The images on the graphic memory 26 are displayed on the display unit 5.
Since the conventional traffic information display system is constructed as above, the following problems have been involved therein:
(1) A complicated road map is displayed on the display unit 5, so when this display is presented to the vehicular driver, it is not easy for the driver to recognize the present position of the vehicle. Particularly, since the on-vehicle display is mounted in the peripheral portion of the dash board so as not to be an obstacle to driving and so as to facilitate the driver's recognition of the display, the display size is 6 to 9 inches at most, thus making it more difficult for the driver to recognize the present position.
(2) Since the destination of the road along which the vehicle is running is not displayed on the display unit 5, the driver feels uneasy. When the destination is to be displayed in the conventional system, it is required to retrieve line data, letter data, etc. in the map data through a complicated process.
(3) Since only two-dimensional displays are made on the display unit 5, it is impossible to distinguish between an at-grade intersection and a solid intersection (grade separation), so the driver cannot recognize the identity between the display on the display unit and the outside scenery, sometimes resulting in the driver feeling uneasy.